Portable, hand held, and/or disposable devices used to perform real time or near-real time medical, chemical, or biological assays may enable a user of the device, to apply one or more reagents to a sample taken from a subject (e.g., urine, saliva, feces, genitals, ear, wound, etc.). The user may perform an assay on the sample by causing the device to deliver the one or more reagents to the sample (e.g., to test for the presence of certain biological matter, chemicals, contaminants, etc.). However, a device may not properly separate reagents from one another or apply the reagents in a manner and/or order than is intended for the assay. Accordingly, the assay may be performed incorrectly, produce unreliable results, and/or waste a limited number of samples available for testing.